Many different types of printing have been invented, a large number of which are presently in use. The known forms of print have a variety of methods for marking the print media with a relevant marking media. Commonly used forms of printing include offset printing, laser printing and copying devices, dot matrix type impact printers, thermal paper printers, film recorders, thermal wax printers, dye sublimation printers and ink jet printers both of the drop on demand and continuous flow type. Each type of printer has its own advantages and problems when considering cost, speed, quality, reliability, simplicity of construction and operation etc.
In recent years, the field of ink jet printing, wherein each individual pixel of ink is derived from one or more ink nozzles has become increasingly popular primarily due to its inexpensive and versatile nature.
Many different techniques on ink jet printing have been invented. For a survey of the field, reference is made to an article by J Moore, “Non-Impact Printing: Introduction and Historical Perspective”, Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).
Ink Jet printers themselves come in many different types. The utilization of a continuous stream of ink in ink jet printing appears to date back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hansell discloses a simple form of continuous stream electro-static ink jet printing.
U.S. Pat. No. 3,596,275 (Sweet et al) also discloses a process of a continuous ink jet printing including the step wherein the ink jet stream is modulated by a high frequency electro-static field so as to cause drop separation. This technique is still utilized by several manufacturers including Elmjet and Scitex (see also U.S. Pat. No. 3,373,437 (Sweet et al)
Piezoelectric ink jet printers are also one form of commonly utilized ink jet printing device. Piezoelectric systems are disclosed by Kyser et. al. in U.S. Pat. No. 3,946,398 which utilizes a diaphragm mode of operation, by Zolten in U.S. Pat. No. 3,683,212 which discloses a squeeze mode of operation of a piezoelectric crystal, Stemme in U.S. Pat. No. 3,747,120 discloses a bend mode of piezoelectric operation, Howkins in U.S. Pat. No. 4,459,601 discloses a piezoelectric push mode actuation of the ink jet stream and Fischbeck in U.S. Pat. No. 4,584,590 which discloses a shear mode type of piezoelectric transducer element.
More recently, thermal ink jet printing has become an extremely popular form of ink jet printing. The inkjet printing techniques include those disclosed by Endo et al in GB 2007162 and Vaught et al in U.S. Pat. No. 4,490,728. Both the aforementioned references disclosed ink jet printing techniques that rely upon the activation of an electrothermal actuator which results in the creation of a bubble in a constricted space, such as a nozzle, which thereby causes the ejection of ink from an aperture connected to the confined space onto a relevant print media. Printing devices utilizing the electro-thermal actuator are manufactured by manufacturers such as Canon and Hewlett Packard.
As can be seen from the foregoing, many different types of printing technologies are available. Ideally, a printing technology should have a number of desirable attributes. These include inexpensive construction and operation, high speed operation, safe and continuous long term operation etc. Each technology may have its own advantages and disadvantages in the areas of cost, speed, quality, reliability, power usage, simplicity of construction operation, durability and consumables.
Many inkjet printheads are constructed utilizing micro-electromechanical systems (MEMS) techniques. As such, they tend to rely upon standard integrated circuit construction/fabrication techniques of depositing planar layers on a silicon wafer and etching certain portions of the planar layers. Within silicon circuit fabrication technology, certain techniques are better known than others. For example, the techniques associated with the creation of CMOS circuits are likely to be more readily used than those associated with the creation of exotic circuits including ferroelectrics, gallium arsenide etc. Hence, it is desirable, in any MEMS constructions, to utilize well proven semi-conductor fabrication techniques which do not require any “exotic” processes or materials. Of course, a certain degree of trade off will be undertaken in that if the advantages of using the exotic material far out weighs its disadvantages then it may become desirable to utilize the material anyway. However, if it is possible to achieve the same, or similar, properties using more common materials, the problems of exotic materials can be avoided.
An important aspect of any inkjet printer is printhead maintenance. Printhead maintenance increases the lifetime of a printhead and enables the printhead to be used after idle periods. Typical aims of printhead maintenance are the removal of particulates from the printhead, removing ink flooded onto the printhead face, and unblocking of nozzles which may become blocked with ink (‘decap’) or particulates. Hitherto, a variety of techniques have been used for printhead maintenance, such as suction cappers and squeegee-type wipers.
However, the usual problems of printhead maintenance are exacerbated in the Applicant's pagewidth printheads, which have high-density nozzles constructed on a silicon wafer using MEMS techniques. Whilst these printheads are very inexpensive to manufacture, they are typically less robust than other inkjet printheads and, hence, have hitherto required special consideration of printhead maintenance. Accordingly, the Applicant has proposed a number of novel techniques for printhead maintenance, including non-contact maintenance techniques. Some of these maintenance techniques are exemplified in U.S. application Ser. No. 11/246,688 (filed Oct. 11, 2005); Ser. No. 11/246,707 (filed Oct. 11, 2005); Ser. No. 11/246,693 (filed Oct. 11, 2005); Ser. No. 11/482,958 (filed Jul. 10, 2006); and Ser. No. 11/495,815 (filed Jul. 31, 2006), the contents of each of which are herein incorporated by reference.
It would be desirable to provide a MEMS pagewidth printhead, which is amenable to a plethora of printhead maintenance techniques, including contact maintenance techniques. It would be further desirable to provide a MEMS printhead having superior mechanical robustness. It would be further desirable to provide a MEMS printhead, which traps a minimal number of particulates and hence facilitates printhead maintenance.